Well drilling system



Jan. 7, 1936.

N. WILKINSON WELL DRILLING SYSTEM 3 Sheets-Sheet 1 Original Filed June29, 1933 Jan. 7, 1936. I w soN 2,026,600

WELL DRILLING SYSTEM Original Filed June 29, 1933 3 Sheets-Sheet 2 Jan.7, 1936. w 5 N 2,026,600

WELL DRILLING SYSTEM Original Fild June 29, 1933 s sheets-sheet 5Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE 2,026,600 WELLDRILLING SYSTEM Application June 29, 1933, Serial No. 678,235 RenewedFebruary 13, 1935 22 Claims.

This invention is in part a continuation of the application of NathanWilkinson, Serial No. 512,899, filed February'Z, 1931, for a Powertransmission system. No claim is made herein to the system of motor andgenerator control of general application herein disclosed inasmuch asclaims of such character .appear in the above identified application andin application Serial No. 10,155, flied March 9, 1935, which is adivision of the present application.

This invention relates to power transmission systems and controltherefor. It may be used in connection with the operation of a powerdriven tool and more particularly in connection with apparatus fordrilling holes. It is especially adapted for use with rotary oil welldrilling rigs.

- A large number of different operating conditions are encountered inthe drilling of oil wells.

Itis accordingly an object of the invention to' provide a powertransmission system which is flexible, enabling it to meet the variedoperating conditions. A more specific object is the attainment of suchflexibility with'a minimum of cost; and also with a maximum ofreliability.

A further object is the provision of an electric power transmissionsystem in which internal combustion engines are used as prime movers,

and further, in which close regulation. of engine speed is not required.A more specific object is the provision of such a system in which twoengines are used each one automatically carrying its proportion of thetotal load.

In connection with oil well drilling apparatus of the type in whichwater is pumped into the drill hole, it is an object to provide a systemof power transmission in'which either the pump motor or the drill motormay be started, stopped and otherwise controlled, without afiecting theother motor.

Still another object isthe provision of a power transmission system inwhich all of the drilling and pumping operations and all of the ordinaryand usual hoisting operations may be performed with either one primemover in operation, or more than one.

Still another object is the provisio'n of a well drilling system inwhich one or more of a plurality of electric motors are used toselectively drive the hoisting, pumping, and drilling mechanism, the

energy for the motors being selectively furnished by one or more of aplurality of engine driven generators which are preferably of diflerentcapacities.

A further object of the invention is the provision of awell drillingsystem in which one or more of a plurality of electric motors are usedto selectively drive the hoisting, pumping, and drilling mechanism, theenergy for the motors being supplied during certain operations from allof a system of the above character with a-plurality I of engine drivengenerators each having a rheostat for controlling the excitation of thefield winding thereof, and more specifically the provision of clutchdevices forrendering all of said rheostats simultaneously operableduring certain operations and for rendering said rheostats operable inpairs during other operations.

Other objects will appear hereinafter as the description of theinvention proceeds.

The novel features of the invention will appear from this specificationand the accompanying drawings showing one embodiment of the inventionand all these novel features are intended to be pointed out in theclaims.

. In the drawings:

Fig. 1 is a diagrammatic showing of one embodiment of the invention withparticular rela-. tion to the electrical control features thereof.

Fig. 2 is a more or less diagrammatic elevation of mechanical featuresof one type of oil well drilling rig in connection with which theinvention may be used.

Figs. 3 to '7 inclusive are diagrams of various electrical powerconnections which may be obtained with the system shown in Fig. '1.

Fig. 8 is a diagrammatic showing of an improved embodiment of theinvention with particular relation to the electrical control featuresthereof.

Figs. 9 to 13 are schematic diagrams showing various electrical powerconnections which may be obtained with the system shown in Fig. 8.

Referring to Fig. 1' of the drawings a prime mover I is here shown asconnected to a pair of i generators 2, 3. The generator 2 is diagramitsterminals connected respectively to conductors 9 and Ill. The embodimentof the system here shown includes a pair of intermediate conductors II,II. The conductor II is connectable to the conductor 1 by means of acontactor l3, and is also connectable to the conductor 3 by means of acontactor I4. The conductor I2 is connectable to the conductor 3 bymeans of a contactor I5, and is also connectable to the conductor I. bymeans of a contactor it.

Where two sets of engines and generators are 'utilized as in theillustrative embodiment, the

generator 5 may have one of its terminals connected to conductor 3 andthe other terminal maybe connected to a conductor H. The generator 8 mayhave one of its terminals connected to conductor I3 and the other to theconductor l1.

It will be evident as the description proceeds that more than two setsof engines and generators may be utilized. Where two or more sets ofgenerators are used, the generators of like capacity may be used inseries.

A pair of conductors I 3, I3 is provided which are connectedrespectively to the blades of switches 23, 2| which are both of thesingle pole double throw type. The switch 23 is adapted to connect theconductor l8 to either he conductor 1 or the conductor 3. The switch 21is adapted to connect the conductor It to either the conductor 3 or theconductor l1.

The conductor I3 is connected, through a time element overload relaycoil 22, to a bus 23. whereas the conductor I3 is connectable through acontactor 24 to a bus 28. One or more motors may be connected to thebuses 23, 23, two motors 26, 23 being here shown. The motor 23 isconnectable to buses 23, 25 by a switch 21, operating in unison withwhich is an auxiliary contact 53 for a purpose which will appearhereinafter. The motor 28 is connectable to the buses 23, 25 by a.switch 23 which-also includes an auxiliary switch Another motor 33 ishere shown as having its terminals connected to the blades of a pair ofsingle pole double throw switches 3|, 32 respectively. The switch 3| isadapted to connect one terminal 01' motor 33 to either the conductor Hor the conductor l2. The switch 32 is adapted to connect the otherterminal of motor to either conductor 12 or to conductor 11. Interposedin one of the conductors leading from one of the terminals of motor 30is the coil of a time element overload relay 33 which is in a circuit tobe described hereinafter.

An exciter 33 is here shown as connectable to the buses 34, 35 whichserve to feed the operating coils oi the various contactors and thefield windings of the generators and motors'as will be described indetail.

The field windings 4|, 44 of the generators 2 and I respectively arehere shown as controllable by a pair of reversible potentiometerrheostats 31, 33 respectively. One set of terminals of the potentiometerrheostats 31, 33 are connected by means of a conductor 33 through thecontacts of the overload relay 22, to the bus 34. The other set ofterminals oi the rheostats 31, 33 are connected to the bus 35.- Themovable contacts of rheostat 31 are connected by means of conductors 33,43 to the terminals of field winding 4|, which latter is here shown asshunted by a resistance or rheostat of any desired form. The

movable terminals of rheostat 33 are connected by means of conductors.42, 43 to the terminals of field winding 44, which is also here shownas shunted by a resistance or rheostat. For many of the conditions ofoperation the movable members of rheostats 31 and 33 may be operated inacaaeoo unison but it it is desired to operate these rheostatsseparately a coupling Ill may be disengaged. Operable in unison withrheostat 38, and of course with rheostat 31, is shown a contact 45cooperable with a ring contact 48. The contact 5 45 is connected to thebus 35. The ring contact 46 has a gap 41 therein in such position thatwhen the rheostats 31, 33 are in thefofl position the contact 45 doesnot engage the ring 46. For the sake of simplicity only one ring 46 andcontact 45 0 have been shown butii desired there may be one such ringand contact not only for rheostat 33 but also for rheostat 31, thisbeing a mere duplication oi parts.

The ring 46 is connectable through conductors 15 43, 43 and theauxiliary switch 53 to one terminal of a field winding SI for the motor28. The other terminal of the field winding ii is connected to bus 34.The ring 43 is also connectable through a conductor 52 and the aux- 20iliary switch 53 to a field winding 54 of the motor 26, the otherterminal of said field winding being connected to bus 34. The conductor43 is connected by a conductor It! to a contact 33 with which latterblade 3| of switch C is cooperable.

The field windings 64 and 64 of generators 3 and 6 respectively are alsohere shown as controllable by reversible potentiometer rheostats 51 and58 respectively. One set of terminals of the resistances of therheostats 51, 53 are connectable 0 by means of a conductor to the bus34. The other set of terminals of said resistances is connected to bus35. Interpcsed in the conductor 55 are the contacts of the overloadrelay 63 and the contacts oi. a relay 53. The movable contacts 0t 35rheostat 51 are connected by conductors 53, 60 to the terminals of fieldwinding ii, and the movable contacts of rheostat 53 are connected byconductors 62, 63 to the terminals of field winding 64. Said fieldwindings may be shunted by resistances m as shown. Similarly asdescribed in connection with rheostats 31 and 33, there is here shownone contact ring 66 with which a contact 35 operable in unison withrheostat 53 cooperates. The ring 66 also has a gap 61 so that when therheostat 53 L5 (or the rheostat 51) is in the ofi." position, thecontact will be out of engagement with the contact 33. A coupling 2 mayalso be provided between the rheostats 31 and 58 for reasons as statedin connection with rheostats 31 and 33. 30 The ring 36 is connectedthrough a conductor HI to a contact 34 of a master control switch C. Thecontact 35 is connected to the bus 35.

Cooperable with contact 34 is a switch blade ll of master switch C,which blade is connected by 56 means of a conductor 63 to one terminalof a field winding 10 for the motor 30. The other terminal of said fieldwinding is connected to the bus 34, and said field winding may also beshunted by a resistance as shown. 60

The operating coil ior contactor 53 has one terminal connected toconductor 55 and the other terminal connected through a contact 1| tothe bus 35. The contact 1| is controlled by means of a lever 33 whichwill be further described here- 55 inaiter in connection with Fig. 2.

The operating coils of contactor-s l3 and II are here shown as inparallel and interposed in a conductor 12 one end of which is connectedto bus 34 and the other end of which is connected to a contact 13 of themaster control switch C.

A blade 14 of the switch C is connected to bus 35, and is cooperablewith contact 13.

The operating coils of contactors l4 and ii are here shown as inparallel and interposed in a conductor 15 one terminal of which isconnected to bus 34 and the other terminal of which is connected toacontact 16 of the switch C. The blade 14 of the switch C is alsocooperable with the contact 16.

The operating coil of contactor 24 is interposed in a conductor 19 oneterminal of which is connected to bus 34 and the other of which isconnected to a contact 18 of the. switch C. Cooperable with contact 18is a blade 11 of the master switch C. The blade 11 is also electricallyconnected by conductor 60 with the blade 14, and therefore also to bus35.

For a purpose which will appear in connection with the description ofthe operation of the system, a switch 85 is provided for bypassing thecontactor 24. The switch is, under the usual operating conditions, open.

Referring now to Fig. 2, this shows in more or less diagrammatic form anoil well drilling rig of the rotary type with which the invention may beutilized. It is to be understood that the particular form of mechanicaldrilling rig is shown only by way of illustration so that one way inwhich applicant's invention may be utilized may be better understood.The drilling rig here shown comprises a hollow drill 86 around which'isdisposed a casing 81 which is sunk around the drill as the drillingproceeds. The drill 86 may be rotated in any suitable manner by means ofa gear 88 driven by a bevel pinion 89 from a shaft 90. The

shaft 90 may be connected to a driving chain 92 by means of a clutch 9|operable by a lever 95.

The driving chain 92 is in operative relation to a shaft 93 which is inturn driven by a driving chain 94 from the motor 30 which corresponds tothe motor 30 in Fig. 1. A shaft 96 is provided which carries fastthereon a winding drum 91. The shaft 96 may be connected to a drivingchain I by means of a clutch 98 operable by a clutch lever 99. Theclutch lever 99 is operatively related to the switch H which correspondsto the switch of same number in Fig. i, and it will be apparent thatwhen the clutch 98 is disengaged the switch H is closed. A brake IOI isprovided for the drum 91, which brake is operable by means of a brakelever I02.

The winding drum 91 is adapted to receive a cabie I03 which runs to thetop of a derrick I04 and is )flSSCd over suitable-pulley blocks orsheaves at th: top of the derrick and also over a sheave operativelyrelated to the drill rod 86, so that the winding drum 91 may be used tohoist and lower the drill rod 86, or other desired parts. The drill rodis here shown as connected by means of a flexible hose I to a pipe I06,in turn connected to a pair of pumps I01, I08 of any suitable form. Thepumps are here shown as driven respectively by the motors 26, 28 whichcorrespond to those of the same number in Fig. 1.

The operation of the system will be best understood by a considerationof various power set- I ups that may be secured therewith.

If it is desired to hoist the drill rod 86, or any other part attachedto the hoisting cable I03, at full speed, the motor 30 is connected tothe large generators 2, 5 in series, as indicated in Fig. 3, as follows:It is assumed that the exciter 33 is connected to the buses 34, 35, andthat the hoisting drum 91 is connected to the shaft 93 by means of theclutch 98. The switch 3I is thrown to its upper contact and the switch32 to its lower contact. The master switch C' is thrown to the left, asviewed in the drawings, thereby connecting I the blades 14 and 8| to thecontacts 13 and 83 respectively. It will be noted, incidentally, thatthe contact with which the blade 11 contacts, in this position, is, inthe illustrative embodiment, a dead contact. With the master switch C inthe position stated the contactors I3 and I5 have their operating coilsenergized and are closed. It may be noted that in the illustrativeembodiment and in the particular set-up now under consideration thecontactor I5 will not be in any circuit. It will be also noted thatwhile the blade 8| is in engagement with the contact 83 the fieldwinding circuit for the motor 30 is not as yet completed since thecontact 45 is, in the starting position, not in contact with the ring46. The generator field winding rheostats 31, 38 may now be operated toincrease the electromotive force generated by generators 2 and 5. alsothereby closing the field winding circuit for motor 30. It

is of course clear that the motor 30 will operate in adirectiondependent upon which direction the rheostats 31 and 38 havebeen moved. The provision of differential series field windings H3, H4for generators 2, 5 respectively, gives these machines .droopingcharacteristics, which coacts with the method of speed control of motors30, 26 26 and 28 by generator field excitation to give good startingtorque and acceleration control.

With the set-up of Fig. 3 described above the motor which may be say a400 H. P. motor operating at'1000 R. P. M. at 350 volts with a 30 peakload of say 600 H. P., is fed from the two large generators which aresay of 200 k. w. capacity each operating at 1200 R. P. M. and gencrating175 volts each. The engines I, 4 are rated at 385 H. P. each at 1200 R.P. M. The foregoing figures are given merely by way ofex ample as arealso the ratings of other machines ""to be hereinafter noted. It will beobviousthat the invention is in no way limited to the selection or useof machines of the ratings, voltages and speeds herein given and thatthose skilled in the art may easily make a choice of ratings etc.suitable to meet any particular conditions. The ratings given in thisspecification are cited merely to further bring out the possibilitiesand- 5 flexibility of the disclosed system.

The engines I and 4 are provided with the usual governors (not shown) sothat if desired the speeds of these engines may be kept at substantially12 00 R. P. M., as in the above cited example, or at any other selectedspeed, as will be understood by those skilled in the art.

If it is desired to hoist at half speed the electrical set-up of Fig. 4may be secured, by throwing both the switches 3I and 32 to their upperpositions. The mechanical set-up of the parts of Fig. 2 are the same asdescribed in connection with the set-up of Fig. '3, and the masterswitch is also in the same position. It will be noted, however, thatsince in the set-up of Fig. 4 the motor 304s operating from generator 2only, that the contactor I5 is now in the circuit feeding motor 30. Withthis set-up the engine I is the only one in operation-and may operate asbefore with 385 H. P. at 1200 R. P. M. The 200 k. w. generator 2 nowfeeds the motor 30 at 175 volts and therefore the motor runs at halfspeed. that is, 500 R. P. M.

If for any reason it is desired to hoist at half speed with the,motor 30fed from generator 5, 71) the electrical set-up will be the same as inFig.

4, but to secure the same the switches 3I and 32 are both thrown ontotheir lower contacts. The contactor I5 is here again in circuit with themotor 30, and of course the master switch C remains in the same positionas for the set-up in Figs. 3 and 4.

It will be noted that with the hoisting set-ups as hereinbeforedescribed in which the lever 88 has been thrown to cause engagement ofthe clutch 88, the switch 1| is opened, thereby deenergizing thecontactor 58. The opening of this contactor opens the circuit ofrheostats 81 and 88 and prevents current from being fed to the fieldwindings of generators 8 and 8.

If it is desired to rotate the drill 88 and pump water down through thedrill at the same time, the clutch 88 is thrown out (thereby closingswitch 1|) and the clutch 8| is thrown in so as to connect the drivingshaft 88; for rotating the drill, to the shaft 88. The switch 8| isthrown to its upper position and the switch 82 is thrown to its lowerposition. The switches 28 and 2| are thrown respectively to their upperand lower positions. The master switch C is thrown to its right handposition, thereby energizing the operating coils of contactors I4 andIt, by reason of the engagement of blade 18 with contact 16. It will beincidentally noted that contactor It will not be in any circuit in thisparticular set-up. The engagement of blade 11 with contact 18 energizesthe operating coil of contactor 24. If it is desired to use both pumpsI81 and 188, both switches 21 and 28 are closed thereby connecting thearmature circuits of motors 28 and 28 to the conductors 1 and I1. Whilethe auxiliary switches 88 and 58 are closed it will be noted that thecircuits for the field windings 58 and 8| are incomplete since at thestart contact 45 is not in engagement with ring 48. The rheostats 81 and88 may now be operated in the proper direction thereby causing thegenerators 2 and 5, in series, to feed the pump motors 26, 28 as shownin Fig. 5. Inasmuch as the contact 1| is closed, the relay 88 isenergized and therefore operation of the rheostats 51, 58 will supplycurrent to the field windings of generators 8 and 8. The engagement ofcontact 88 with ring 88 causes the field winding 18 of motor 88 to besupplied with current.

It will be evident that with the set-up of Fig. 5 the motor 88 may beused at full speed for the drilling operation since it is fed from thegenerators 8 and 8 in series. By way of example, the generators 8 and 8may be of 40 k. w. capacity each at a voltage of 125. For this drillingand pumping operation the engines 1 and 4 mayhave their governors set tooperate at say 850 R. P. M., the engines producing at that speed say 280H. P. The motor 88 may then operate at say 710 R. P. M. at 250 volts andproduce say 100 H P. The larger generators 2 and 5 operating at 850 R.P. M. at 125 volts may produce say 142 k. w. Each of the pump motors 28,28 may-be rated at say 276 H. P. at 850 R. P. M., noting that adequatepumping capacity may be obtained by using either one of the pumpingunits; however, from the above data it is apparent that there isadequate generator capacity for the other pumping unit to be operated atthe same time with reduced output for mixing mud", if desired. It willbe obvious of course that with the machines in the cited example, thepower produced and consumed may be widely varied by adjustment of therheostats 81, 88 and. 81, 58.

If the operator should for any reason, while the system is operatingwith the set-up of Fig. 5

hereinbefore described, attempt to use the hoist drum 81 by throwing theclutch 88 into enaosaeoo deenergizing contactor 88 and consequentlydeenergizing the field circuits of the generators 8 and 8, to which themotor 88 is at that time connected.

If it is desired to drill and pump at half speed. 5 the set-up of Fig. 6may be secured as follows: The mechanical set-up in connection with Fig.8 may be the same as in connection with Fig. 8. The switches 8| and 82are both thrown to their upper positions, and the switches 28 and 2| are10 likewise both thrown to their upper positions. The master switch Cremains in its right hand position as described in connection with thesetup of Fig. 5. By operation of the rheostat 88 the motor 88 may now befed from generator 815 through contactors l4 and I8 while either of themotors 28, 28 may be fed from generator 2. The voltage of generator 2may of course be controlled by rheostat 81. For this set-up the enginepreferably has its governor set for a lower speed as in case of the halfspeed hoisting set-up of Fig. 4. The pump motor 28 may now operate witha rating of say 137 H. P. at 425 R. P. M. since it is fed from onegenerator at 125 volts. The drill operating motor 88 may produce say H.P. at 355 R. P. M. being also fed at say 125 volts from generator 8.

It sometimes occurs that it is desirable to hoist and pump at the sametime. For this purpose the fishing set-up, as shown in Fig. 7, may be 0obtained. with this set-up hoisting operations may be performed as incase a drill rod should break, and at the same time one of the pumps maybe used. This fishing setup may be secured with a pump motor fed fromgenerator 2 and the motor 88 fed from generator 8 or vice versa. Theoperations for securing the set-up shown in Fig. 7 will first bedescribed. The clutch 88 is thrown in and if it is desired to hoistonly, the clutch II is thrown out. The switches "40 and 82 are boththrown to their lower positions. The switches 28 and 2| are both thrownto their upper positions. The master switch C is thrown to its left handposition thereby causing closure of contactors I 8 and I8. The switch 88is closed-i5 by hand, in the illustrative embodiment, to thereby connectthe bus 28 to the blade 2|. -It will be noted that with the masterswitch in its left handposition the bypassing of contactor 28 isnecessary since in that position of the master so switch the coil ofcontactor24 is not energized. The switch 21 for pump motor 28 is closedand the rheostats 81 and 88 operated either separately or in unison asdesired. For this set-up the engines I and 4 may have their governors toset to causeoperation of the engines at substantially 1200 R. P. M., forexample. The pump motor 28 may then operate at say 590 R. P. M. with arating of 192 H. P., being fed from the generator 2 operating with arating of 200 k. w. at 1200 R. P. M. The motor 88 operates at a ratingof say 200 H. P. at 500 R. P. M. from the generator 8 operating at arating of 200 k. w. at 1200 R. P. M.

If for any reason it is desired to operate the motor 88 from generator 2and a pump motor from generator 5, the switches 8| and 82 are boththrown to their upper positions and the switches 28 and 2| are boththrown to. their lower positions. The master switch remains in its lefthand position and the remaining operations are similar to thosedescribed in connection with Fig.

If for any reason it is desirable to rotate the gagement, the contact 1|will be opened thereby drill as it is being hoisted, or lowered. withfor example the fishing set-up of Fig. '1, the clutch 8| may be throwninto engagement.

In general, it will be apparent that current will not be supplied toeither of motors 26, 28 unwhich is true irrespective of the position ofthe master switch C. When the rheostats 51, 58 only for the smallergenerators 3, 6 are on field current can be obtained for the motor 38only if the master switch C is in its right hand position, which is theposition for the normal drilling operation. When the rheostats 31, 38only are om-current can be obtained for the field windings of the pumpmotors provided the switches for these motors are respectively closed,and current can be obtained for. the field winding of motor 38 providedthe master switch C is in its left hand position which is the hoistingposition.

It will be obvious that if desired, particularly in connection with theset-ups. of Figs. 4, 6 and '1,- the rheostat for generator 2 may beoperated separately from the rheostat for generator by simplydisengaging the coupling III, and particularly in the case of Fig. 6 therheostat for generator 3 may be operated separately from that forgenerator 6 by disengaging the coupling 2.

It will be evident from the description of the various set-ups that ifdesired only one engine and one set of generators need be used, ifdesired, for the first few thousand feet of drilling (the set being sayas in Fig. 6) and that subsequently, or at any desired time, more thanone engine and set of generators may be used for drilling (the set-upbeing say as in Fig. 5). It is of course obvious that the same appliesat any stage of the drilling since if one engine fails, operations maybe carried on with the other engine but with the driving motorsoperating at half speed. Full torque is however available whether themotors are running .at full speed or half speed.

Moreover to secure this full torque under either i condition ofoperation it is unnecessary to alter the driving or gear ratio asbetween the driving motors and the mednanical drill rigging.

What has been stated above also applies with regard to the fullspeed andhalf speed hoisting set-ups of Figs. 3 .and 4 respectively.

The exciter 33 being separately driven by an auxiliary engine (notshown) makes possible the use of said exciter for various purposes, suchas for lighting the drill site, without necessity of having the mainengines I, 4, running, or even before said main engines are available atall as while the drilling rig .and drive are being erected. Referringnow to Figure 8 of the drawings a prime mover I is arranged to drive apair of generators 2 and 3 which are diagrammatically indicated as ofequal capacity. Another prime mover 4 is arranged to drive .a pair ofgenerators 5 and 6 which are diagrammatically indicated as of equalcapacity. Generators 2 and 5 are permanently connected in series notingthat the outer terminals of these generators .are connected toconductors I20 and I22 and that the intermediate terminals are connectedto commonconductor I2I. Generators 3 and 6 are permanently connected inseries noting that the outer terminals of these generators are connectedto conductors I23 and I24 and that the intermediate terminals areconnected to common conductor I2I. Generators 2 and 5 are provided withseries difKeren-Y tial field windings H3 and H4, self excited fieldwindings I48 and HI and separately excited fiel windings H and 44,respectively. Generator and 6 are provided with differential seriesfielwindings I42 and I43, self excited field winding I44 and I45, andseparately excited field windings 64 and 6|, respectively. Theseparately excited field windings and the self excited field windingsare normally cumulative. ing of each generator is so proportional thatits ampere turns are always less than the air-gap ampere turns, that is,the resistance of this winding is such that theplotted curve (current inself excited winding as abscissa and terminal voltage as ordinate) neverintersects the voltage characteristic curve of the generator. Thepolarity and magnitude of generator voltages are therefore determined bythe separately excited windings. The main purpose of the self excitedand the series differential field windings is to accentua'te thedrooping characteristic of the generators so as to prevent the stallingof a prime mover in event one prime mover is temporarily unable todevelop as much torque as the other 25 prime mover. That is, stalling ofan imperfectly operating prime mover is prevented by theautomaticweakening of the self excited field windings of the generatorsconnected thereto upon occurrence of the reduction in speed of thefaulty prime mover. Electromagnetic oontactors I and I36 are provided toconnect series connected generators 2 and 5 in parallel with seriesconnected generators 3 and 6.

Pump motors 26 and 28 may be selectively connected to load conductors.23--25 by means of switches 21 and 29. An electromagnetic contactor 24is operable to connect load conductor 25 with the blade of switch 2 I,noting that load conductor 23 is permanently connected to the blade .ofswitch 28 through the coil of overload relay 22.

By means of hand operated switches 28 and 2| the load conductors 23 and25 may be selectively connected either to conductors I8 and I2 I orconductors- I9 and I2I, or to conductors I8 and I8, as hereinbeforedescribed in connection with Figure 1.

The drilling or hoisting motor 38 may be selectively connected toconductors I25 and I, or

I26 and I2], or to conductors I25 and I26 by means of hand operatedswitches 3| and 32 in substantially the same manner as described inconnection with Figure 1.

Separately excited field windings 4|, 44, 64 and 6| are controlled byrheostats 31, 38, 58 and 51 respectively. These rheostats .are, allenergized from bus 3435 through conductors I50 and I5I when overloadrelays 22 and 69 are in their normally closed positions. An overload oneither motor 38 or the pumping motor 26 or 28 will cause the respectiveoverload relay 69 or 22 to ope ate to deenergize all of the separatelyexcited generator field windings. Rheostats 31 and 38 are mechanicallyconnected together by clutch III and rheostats 51 and 58 aremechanically connected together by clutch I I2 in the same manner asdescribed in connection with Figure 1. An additional clutch I52 isarranged between rheostats 38 and 51 so that all four rheostats may besimultaneously operated or, if clutches ,I II and I '2 are disconnected,so that rheostats 38 and 51 may be operated simultaneously. Anadditional clutch I53 is arranged between rheostats 31 and 58, so thatwith clutches I I I and I I2 disconnected, rheostats 31 and 58 may besimultaneously oper- The self excited windlo ated. The utility of thisarrangement will be better understood in connection with the descriptionof the operation of the generators durin certain operations. a

Master controller C is a double pole, double throw switch having bladesI6I and I62. When these blades are thrown to their left hand position acircuit is established from bus 65 I66, through conductor I61 to bus 64.

conductor 60, switch blade I62, conductor I64,-

operating coil or contactor I66, and through conductor I61 to bus 64.The closure of contactors I65 and I66 connect the generators inseriesparallel. When the blades of the master controller C are moved totheir right hand position a control circuit is established from bus 65through conductor I60, conductor 66, switch blades I6I, conductors 19,the operating coil of contactor 24 to bus 34 thereby causing contactor24 to close. Another circuit is also established from bus 35 throughconductor I60,'conductor 60, switch blade I62, conductor I34, operatingcoil of contactor The closure of contactors I66 and 24 connectsgenerators 2, 5 and 6, 6 to motor 25 (or 26) and motor I0 respectively.

Inasmuch as motors 26, 26 and 60 are used in close proximity toexplosive gases it is necessary that these motors be totally enclosedand for this reason each of these motors is provided with a .iorceddraft ventilating system. For example,

motor 26 is provided with a blower motor I55 which is connected acrossthe field winding 54 and field control rheostat I 56. Pump motor 26 isprovided with a blower motor I51 which is connected across field winding5I and field control rheostat I56. Motor 60 is provided with a blowermotor I56 which is connected across field winding I0. It is to be notedthat by connecting these ventilating motors across the respective fieldwindings of the motors to be cooled that considerable saving is obtainedin the number of conductors necessary.

All or the generators of this system of Fig. 8 being 01' ample capacity,as distinguished from the system of Fig. l, where the generators 6, 6

are of reduced capacity as compared with the generators 2, 5, the samenecessity is not present for provisions, such as the switch 'II,actuated with the hoist clutch 66, for preventing operation of the motor66 for hoist-driving purposes when supplied from any particulargenerator or generators.

The operation of the system will be best understood by a considerationof the various mechanical set-ups and electrical circuits that may besecured with the system hereinbeiore described.

If it is desired to hoist the drill rod 66 or any other part attached tothe hoisting cable I66, at full speed, the field rheostats should bemoved to such a position that the clutches I I I, I I2 and I52 may bemoved to their engaging positions. With the rheostats all simultaneouslyoperable the voltages of the generators will be substantially equalwhich is a prerequisite to the operation of these generators inparallel. The switch 6I is moved to its upper position and the switch 62is moved to its lower position thereby connecting motor 66 to conductorsI25 and I26. The master controller C may then be moved to its left handposition thereby connecting generators 2, 6. 5 and 6 in series-parallelas schematically shown in Figure 9. The field rheostats 61, 66, 51 and56, are then moved in one direction or the other from their neutralposition to simultaneously raise the voltage or all generators andthereby cause motor 5 60 to start and run in one direction or the other.

With the hoisting set-up shown in Figure 9 above described the motor 66may be of 400 H. P. rating operating at 1,000 B. P. M. at 350 volts witha peak load capacity of 600 H. P. noting that since 10 each generatormay, for example, be of k. w. rating that 600 k. w. will be availablefor hoisting. The ratings 01 the generators and motors are merely citedto more clearly set forth the utility oi the invention and are notintended to be taken 15 in a limiting sense.

It a break down occurs on one of the prime .mover units hoisting at haltspeed may be obtained by connecting motor 66 to the parallel connectedgenerators of the remaining unit by 20 means of switches 6| and 62 asschematically shown in Figure 10, noting that with this connection 300k. w. of generatingcapacity will be available for operating motor 66 atabout hall speed. 25 If it is desired to rotate the drill 66 and pumpliquid down through the drill at the same time, the clutch 66 of Figure2 is disengaged and the clutch 9| is engaged so as to connect. thedriving shaft 66 to the shaft 66 for rotating the drill. 30 The switch6| is moved to its upper position and the switch 62 is moved to its lowposition. I! it is desired to use both pumps I6 and I66, both switches21 and 26 are closed thereby connecting motors 26 and 26 to the loadconductors 26 and 35 25, it is to be noted, however, that adequatepumping capacity may be obtained by using either one 01 the pumpingunits; however, in some instances it is desirable to operate the otherpumping unit at reduced output to mix the liquid which is 40 Pumped intothe casing 01 the well. Switches 26 and 2| are also moved to their upperand lower positions respectively to connect generators 2 and 5 to one orboth of the pumping motors 26 and 26.

The master switch 0 is moved to its right hand 45 position, therebyenergizing the operating coils of contactors I66 and 24, noting that,since contactor I65 is not energized in this position, generators 2 and5 will not be connected in parallel with generators 6 and 6. The circuitconnections for 50 obtaining the above described set-up areschematically shown in Figure 11. Inasmuch as generators 2 and 5 are notelectrically connected with generators 6 and 6 it is desirable thatfield rheostats 61 and 66 be connected together by means 55 or clutchesIII and that rheostats 51 and 56 be connected together by clutches II2,noting that for this set-up the clutches I52 and I56 should bedisengaged so that the above, described pairs 01' rheostats may beindependently operable to w vary the speed of the pumping motors or thespeed of the drilling motor 66 independently.

It will be evident that with the set-up of Figure 11 the motor 66 may beoperated at full speed for the drilling operation (which usuallyrequires 55 3 and 6, namely, 300 k. w. may be used to energize motor30-for drilling operations, yet such is rare- 1y necessary. It will beobvious that the power output of the generators in the above example maybe widely varied to meet the requirements of the conditions byadjustment of the rheostats 31, 38 and 51, 58.

If a breakdown occurs on one of the prime mover units, the drilling andpumping operations may be continued at half speed using the other primemover unit as shown in Figure 12. The position of the clutches 9| and 98will be the same as described in connection with Figure 11. Switches 3|and 32 are moved to connect motor 30 across the operative generator,whether it be 3 or 6, by means of switches 3| and 32. Likewise switches20 and 2| are moved to connect the pump motor or pump motors across thegenerator which remains operative, whether it be 2 or 5. The masterswitch remains in its right hand position as described in connectionwith the set-up of Figure 5. All-of the rheostat clutches (III, II2, I52and I53) are moved to disengaged position so that only the rheostatsassociated with the operative generators may be moved from their neutralpositions to separately control the voltage of the respectivegenerators. It will thus be seen that 150 k. w. will be available forpumping and that 150 k. w. will be also available for drilling atslightly less than full speed by weakening. the field of motor 30 bymeans of normally shunted resistor I60.

It sometimes occurs that it is desirable to hoist and pump at the sametime, noting that this condition is generally known as the fishingset-up. Referring now to Figure 13, with this set-up hoisting operationsmay be performed as in case a drill rod should break, and at the 'sametime one of the pumps may be used. This fishing set-up may be securedwith a pump motor fed from generators 2 and 3 in parallel and the motor30 fed from generators 5 and 6 in parallel or vice versa. Obviously, thefishing operation may be conducted with the set-up shown in Fig. 11 ifdesired. The operations for securing the set-ups shown in Fig. 13 willfirst be described. The clutch 98 is engaged, and if it is desired tohoist only, the clutch 9| is disengaged. The switches 3| and 32 are bothmoved to their lower position and.v switches 20 and 2| are both moved totheir upper positions. The master switch is moved to its left handposition thereby causing closure of contactors I and I36. If it isdesired to operate either one or both-of pump motors 26 and 28 it isnecessary to manually close switch 85 and one or both of switches 21 or29. If for any reason it is desirable to rotate the drill as it is beinghoisted or lowered with, for example, the fishing set-up of Figure 13,the clutch 9| may be moved into engagement.

It is thus seen that Figure 8 is in general similar to Figure 1,however, in order to simplify Figure 8 a. number of the interlockingfeatures described in connection with Figure 1 have been omitted for thesake of clearness, however, it is to be understood that these featuresmay also be used in connection with the system disclosed in connectionwith Figure 8 if desired.

It should be understood that it is not desired .to limit the inventionto the exact details of construction shown and described for obviousmodifications mayoccur to persons skilled in the art.

It is claimed and desiredto secure by Letters H Patent:

1. In an oil well drilling rig of the type having means for hoistingselected parts of the rig and means for operating the drill, two pairsof electric generators, the units of the respective pairs being ofdifferent capacity, a pair of prime movers for driving said pairs ofgenerators respectively, 5 an electric motor, means for connecting saidgenerators of larger capacity in series to said motor and for causingthe latter to effect the hoisting operation at a speed independent ofthe speed of operation of said prime movers, and means for 1 connectingsaid generators of smaller capacity in series to said motor and forcausing the latter to effect the drilling operation at a speedindependent of the speed of operation of said prime movers. l6

2. In an oil well drilling rig of the type having means for operatingthe drill, including a hollow drill rod and a pump for supplying waterto said drill rod, a pair of electric generators of differentcapacities, a prime mover for driving said go generators, an electricmotor for driving said pump, an electric motor for driving said drill, asecond pair of electric generators of substantially the same capacitiesas the generators of said first pair, respectively, a prime mover for 25driving said second pair of generators, a source of separate fieldexcitation for said generators, means for connecting said pump motor toeither or both of the generators of larger capacity and for causingoperation of said pump motor at a.80 speed independent of the speed ofoperation of said prime movers, and means for connecting the drilldriving motor to either or both of the generators of smaller capacityand for causing operation of said drill driving motor at a speed in- 35dependent of the speed of operation of said prime movers.

3. In an oil well drilling rig of the type having means for operatingthe drill including a hollow drill rod and a pump for supplying water tosaid drill rod, two pairs of electric generators, the units of therespective pairs being of difierent capacity, a pair 'ofv prime moversfor driving said pairs of generators respectively, an electric motor fordriving said pump, an electric motor for driving said drill, means forconnecting said generators of larger capacity in series to said pumpmotor, means for connecting said generators of smaller capacity inseries to said drill driving motor, and means for causing said pump anddrill 5 driving motors to operate at a variable speed independent of thespeedof operation of said prime movers.

4. A well drilling rig comprising means for hoisting selected parts ofthe rig, means for drill- Q ing, an electric motor, mechanism operableto selectively connect said electric motor either with said hoistingmeans or with said drilling means.

a pair of electric generators. of different capacities, prime movermeans arranged to drive said generators, and means for connecting saidmotor to the generator of larger capacity when said hoisting means isoperable and to the generator of smaller capacity when said drillingmeans is operable, and for permitting variation of the speed of saidmotor in its hoist and drill driving operations independently of thespeed of operation of said prime mover means.-

5. A well drilling rig comprising means for hoisting selected parts ofthe rig, drilling means, an electric motor, mechanism operable to operatively connect said motor selectively to said hoisting means or to saiddrilling means, a pair of D. C. generators of predetermined capacity, a

pair of D. C. generators of smaller capacity, a

pair of independent prime movers, each oi said prime movers arr nged todrive a generator 01' predetermined capacity and a generator of smallercapacity, and switching means for connecting said generators ofpredetermined capacity in series to said motor when said motor isoperatively connected to said hoisting means and for connecting saidgenerators of smaller capacity in series to said motor and insuringeflective operation of said latter motor supplied by the generators ofsmaller capacity only when said latter motor is out of driving relationto said hoisting means.

6. A well drilling rig comprising means for hoisting selected parts ofthe rig, drill rod rotating means, an electric motor, mechanism operableto selectively connect said motor in driving relation either with saidhoisting means or said drill rotating means or with both of said means,a pair of electric generators of predetermined capacity, a pair ofelectric generators of smaller capacity,

prime movers arranged to drive said generators,

switching means selectively operable to connect said motor across one orboth of said generators of predetermined capacity or across one or bothof said generators of smaller capacity. and means for rendering saidmotor effective for driving purposes when supplied by one or both ofsaid generators of smaller capacity only in case said hoisting means isdisconnected from said motor.

7. A well drilling rig comprising a drill, means for hoisting selectedparts of the rig, means for rotating the drill, an electric motor, meansfor drivingly connecting said motor to said hoisting means or said drillrotating means, a pump arranged to circulate liquid, a second electricmotor for driving said pump, a plurality of electric generators, aplurality of prime movers, an independently driven source of separateexcitation for said generators, means operable to connect one of saidgenerators to supply energy to said first mentioned motor and to connectanother of said generators to supply energy to said second mentionedmotor, and operating connections for insuring selectively that one primemover may drive one of said generators to supply energy to one or saidmotors and another of said prime movers may drive another of saidgenerators to supply energy to another of said motors, or that oneengine may simultaneously drive one generator to supply said hoistingand drilling motor and another generator to supply said pump motor, andmeans operative to control the energy supplied by said generators tosaid motors to insure operation of said motors at speeds independent 01the speed of operation of said prime movers.

8. A well drilling rig comprising a drill, means for rotating andhoisting the drill, an electric motor, means for drivingly connectingsaid motor to said drill actuating means, a pump arranged to circulateliquid, a second electric motor for driving said pump, a plurality ofelectric generators, a plurality of prime movers, means operable toconnect one oi. said generators in energysupplying relation tosaiddrill-actuating motor and to connect another of said generators inenergy-supplying relation to said pump motor, and operating connectionsfor insuring selectively that one prime mover may drive one of saidgenerators to supply energy to said drill-actuating motor and another 0!said prime movers may drive another of said generators to supply energyto said pump motor, or that either engine may simultaneously drive onegenerator to supply. said drill-actuating motor and another generator tosupply said pump motor, and means operative to control the energysupplied by said generators to said motors to insure operation of saidmotors at speeds independent oi the speed of operation oi said primemovers. 5

9. A well drilling rig comprising means for hoisting selected parts ofsaid rig, drilling means, a pump arranged to circulate liquid in thecasing of said well, an electric motor arranged to drive said pump, asecond electric motor, mechanism 10 operable to selectively connect saidsecond motor in driving relation with said hoisting means or saiddrilling means or with both of said means, a pair of series connectedelectric generators, another pair of series connected electric general5tors, two engines each serving as a common driving means for a generatorof each of said pairs and means selectively operable to either connectboth pairs of said generators in series-parallel to said second motor,for hoisting, or to connect 20 said first mentioned generators in seriesto said pump driving motor and to connect said another pair ofgenerators in series to said second motor for drilling and to providefor the operation 01' either motor at diflerent speeds independent oi asthe speed of operation of said engines.

10. A well drilling rig comprising means for hoisting selected parts ofsaid rig, drilling means, a pump arranged to circulate liquid in thecasing of said well, an electric motor arranged to drive 80 said pump, asecond electric motor, mechanism operable to selectively connect saidsecond motor in driving relation with said hoisting means or saiddrilling means or with both of said means, a pair of electric generatorsconnectabie in series, 86 a second pair of electric generatorsconnectable in series, a pair of internal combustion engines eacharranged to drive one of said generators of each of said pairs, andmeans selectively operable either to connect said two pairs of genera 40tors in series-parallel and to connect said second motor to theaforesaid series-parallel connected generators for hoisting or toconnect said generators of one of said pairs in series to said pump Idriving motor to circulate liquid in said casing and as I to connectsaid generators of the other of said pairs in series to said secondmotor for drilling and to render said motors operative at differentspeeds independent of the speed of operation of said engines.

11. A well drilling rig comprising means for hoisting selected parts ofthe rig, an electric motor arranged to drive said hoisting means, a pairoi. electric generators connectable in series, another pair of electricgenerators connectabie in series a pair'oi prime movers each arranged todrive one of said tirst mentioned generators and one 01' said lastmentioned generators, and means selectively operable to-conneot bothpairs of said generators in series parallel to said motor for 00hoisting at full speed or to connect the generators driven by either one01 said prime movers in parallel to said motor for hoisting at haltspeed and to render said motor operative at diiierent speeds independentof the speed oi operation or as said prime movers.

12. A well drilling rig comprising a drill, means for hoisting androtating said drill, an electric motor arranged to drive said hoistingand rotating means, a pair of electric generators connectable in firstmentioned generators and one of said second mentioned generators, andmeans comprising selectively operable switches for connecting thegenerators driven by said engines in seriesparallel and to connect saidmotor to the aforesaid series-parallel connected generators for hoistingor for connecting either one or both of the generators of one of saidpairs to said motor, and for rendering said motor operative at speedsindependent of the speed of operation of said engines. I

13. A well drilling rig comprising means for hoisting selected parts ofthe rig, an electric motor arranged to drive .said hoisting means, apump arranged to circulate liquid in the well, an electric motorarranged to drive said pump, each of said motors having a separatelyexcited field winding, motor driven ventilating blowers arranged tocirculate air through said hoisting and pumping motors, the motors ofsaid blowers being connected across said separately excited fieldwindings respectively, a pair of engine driven electric generators, andmeans operable to selectively connect said hoisting and pumping motorsto said generators respectively and to render said motors operative atspeeds independent of the speed of. operation of said engine drivengenerators.

14. A well drilling rig comprising means for hoisting selected parts ofthe rig, an electric motor arranged to drive said hoisting means, a pumparranged to circulate liquid in the well, an electric motor arranged todrive said pump, a pair of electric generators connectable in series, asecond pair of electric generators connectable in series, each of saidgenerators having a separately excited field winding and individualrheostats arranged to control the excitation of said windings, primemovers arranged to drive said generators, switching means operable toselectively connect said pairs of generators in seriesparallel to saidfirst mentioned motor for hoisting or to connect two of said generatorsin parallel to said hoisting motor and the other two of said generatorsin parallel to said pumping motor for circulating liquid in said well,and means for either connecting all of said rheostats together so as tobe operable simultaneously while said switching means connect all saidgenerators in series-parallel for hoisting or connecting said rheostatsin pairs so that each pair is operable simultaneously and independentlywhile said switching means connect two of said generators in parallel tosaid hoisting motor and connect the other two of said generators inparallel to said pumping motor sa d motors being operative at speedsindependent of the speed of operation of said prime movers throughsuitable adjustment of said individual rheostats.

15. A well drilling rig comprising means for hoisting selected parts ofthe rig, means for drilling, an electric motor, mechanism operable toselectively connect said motor either with said hoisting means or saiddrilling means, a pair of electric generators of different capacities,prime mover means arranged to drive said generators, and means forconnecting said motor to the generator of larger capacity when saidhoisting means is operable and to the generator of smaller capacity whensaid drilling means is operable, said generator of smaller capacitybeing operative to cause said motor to effectively drive said drillingmeans only when said motor is disconnected fromsaid hoisting means.

16. In a well drilling rig oi the type having means for imparting linearmovement to selected parts of the rig and means for imparting rotativemovement to one of saidparts, two pairs of. electric generators, a pairof prime movers for driving said pairs of generators respectively, an 5electric motor, means for connecting a generator of each of said pairsin series to said motor and rendering said motor operative to efiectsaid linear movement, means for connecting the other generator of eachof said pairs in series to said 10 motor and rendering said motoroperative to effect said rotative movement, and means for providing thatsaid motor when operative to eiiect said linear and rotative movementsmay operate at diiferent speeds independent of the speed of 1:;operation of said prime movers.

1'7. In a well drilling rig, an operating element capable of. bothrotative and linear movements,

a pair of electric generators of different capacities, a prime mover fordriving said generators, a 20 second pair of electric generators ofdifferent capacities, a prime mover for driving said second pair ofgenerators, an electric motor operable selectively to impart rotative orlinear movement to said element, means for connecting said motor to oneor both of said generators of larger capacity and renderinglsaid motoroperative at a speed independent of the speed of the prime mover orprime movers driving the generator or generators supplying said motor toeffect linear movement of said element, means for connecting said motorto one or both of said generators offsmaller capacity and rendering saidmotor operative at a speed independent of. the prime mover or primemovers driving said generator or generators supplying-'35 said motor toeffect rotative movement of said element, and means for preventingefi'ective operation of said motor supplied from said generators ofsmaller capacity when said motor is connected to impart reciprocatingmovement to 4 said element.

18. A well drilling rig comprising a drill, means for operating saiddrill to impart linear and rotative movements thereto, a pump forsupplying liquid to said drill, a plurality of prime movers, means forconverting the power of said prime movers and utilizing the convertedpower for driving said drill-actuating, means and said pump, saidconverting means comprising a plurality or separately excited electricalgenerators arranged to be driven by said prime movers, an independentlydriven source of separate excitation for said generators, an electricalmotor arranged to drivesaid drill-actuating means, an electrical motorarranged to drive said pump, and means for providing for the operationof said drill-actuating motor through energy supplied by a plurality ofsaid generators driven by one or more of said prime movers or theoperation 01 each of said motors through energy supplied by anindividual generator while both said generators are driven by either oneof said prime movers, and for varying the speed of operation of eachsaid motor independent of the speed of the other said motor and thespeed of the prime mover or prime movers driving the generator orgenerators supplying energy to said motor.

19. A power plant for drill rigs of the type including a drillingelement adapted to be rotated and hoisted, comprising a plurality ofengines, electro-mechanical means for converting the power of saidengines and utilizing the converted power for driving said-drillingmeans, said. converting means comprising a pair of electrical generatorsarranged in driven relation to. each generators connected in supplyrelation to said motor.

20. A well drilling rig comprising a drill, means for hoisting androtating said drill, an electric motor arranged to drive said hoistingand rotating means, a pump arranged to supply liquid to said drill, anelectric motor arranged to drive said pump, a pair of electricgenerators connectable in series, another pair of electric generatorsconnectable in series, a pair of independent internal combustion engineseach arranged to drive one of said first mentioned pair of generatorsand one of said second mentioned pair of generators, and meanscomprising selectively operable switches for connecting the generatorsdriven by said engines in series-parallel and to connect said hoistdriving motor to the aforesaid seriesparallel connected generators forhoisting or for connecting either generator of one of said pairs ofgenerators to said drill driving motor and either generator of the otherpair of generators to said pump motor to thereby insure operation ofboth of said motors supplied by the generators driven by either engine,and means for render-' ing said motors operative at difl'erent speedsindependent of the speed of operation of said engines.

21. In an oil well drilling rig of the type having means for operatingthe drill including a hollow drill rod and a pump for supplying water tosaid drill rod, a pair of electric generators of diflerent capacities,means for driving said generators, an independently driven source ofseparate field excitation for said generators, an electric motor fordriving said pump, an electric motor for actuating said drill, means forconnecting said pump motor to the generator of larger capacity and forconnecting the drill motor to the generator of smaller capacity and forproviding for operation of each of said motors at different speedsindependent of the speed of operation of the other motor and of thegenerator driving means.

22. A well drilling rig comprising a drill rod, means for actuating saiddrill rod to efiect hoisting and rotation thereof, an electric motor foractuating said latter means, a pump arranged to circulate liquid in thewell, a second electric motor arranged to drive said pump, a pair ofelectric generators, a prime mover arranged to drive both of saidgenerators, an independently driven source of separate excitation forsaid generators, and means for connecting one of said generators to saiddrill-actuating motor and the other generator to said pump motor and forproviding for operation of each of said motors at difierent speedsindependent of the speed 01' the other motor and said generator drivingmeans through variation of the field excitation of the generatorsdriving the several motors.

NATHAN WILKINSON.

